The present invention relates to asynchronous motor control using magnetic induction flux regulation, such flux being able to be the stator, air gap, or rotor flux.
Asynchronous motor control achieved by flux variation under the control of a desired value thereof is known.
Such control requires measurement of the flux, for example the flux in the rotor, which to date is achieved either by providing additional turns on the rotor and then deducing the flux on the basis of the voltage observed at the terminals of the turns, or by measuring stator voltage and current and then deducing the flux from the measurements and from parameters that are characteristic of the motor, using equations that define the operation of the motor.
The first of these methods suffers from the disadvantage of, apart from the fact that practical problems arise in carrying it out, its lack of reliability because of the fact that the flux sensor, which is directly fitted into the motor, is subject to a relatively agressive environment, as regards temperature, humidity, pollution, vibrations, sudden shock, etc.
The second method suffers from the disadvantage that its reliability can be affected by variation in one at least of the said characteristic parameters of the motor, as a function of its thermal status, the parameter most likely to be affected being the stator resistance.
One way of avoiding this disadvantage is to fit a temperature sensor inside the motor but when this is done the same disadvantages as in the first of the above methods are again encountered.
The present invention sets out to provide a method and device for controlling an asynchronous motor by flux regulation that avoids the above disadvantages.